The ability to adjust to changes in the external light environment is especially important to plant survival because, unlike animals, plants depend on sunlight for photosynthesis and they do not have a neuromuscular system which allows them to move to a more optimum light environment. Plants therefore possess the unique light-sensing photoreceptor molecule phytochrome which enables them to perceive the frequent fluctuations of intensity, direction and spectral quality of light in their environment. With the exception of photosynthetic bacteria, phytochrome is found in all photoautrophic organisms from green algae to higher plants. Our studies seek to provide new insight into the structure and evolution of the phytochrome photoreceptor through comparative analysis of the phytochrome genes from representative higher and lower plant species.